We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Printing from Screen Plates 547
tures. Assuming the complementary negative image, the printing process must fulfill the following requirements : behind the uncovered filter elements must be formed the complementary color ; behind white, that is, behind the elements free from protecting silver deposit, there must be black, and behind the completely covered parts, there must be formed white. The pinachromy process (see p. 422), would seem to be the ideal, and it is conceivable that if paper were coated with three suitable leuco-bases, a correct color positive might be formed under the complementary negative. The question is what must be the color of the three leuco-bases. It is evident that they must stand at equal distances in the color circle, for whether subtractive or additive, they must be colorless when in small quantities. The color triad of most screen-plates is pure blue, yellow-green and vermilion, and the complementaries of these are yellow, bluish-red and blue-green.
H. Friese7 suggested that in the reproduction of screen-plates the use of the ordinary filters should be done away with, and the plates themselves stained up, thus for red the plate should be stained green, for the blue an orange, and for the yellow a violet emulsion.
Pinatype Prints from Screen Plates. — L. Didier8 suggested the following procedure for these, and although in connection with Autochromes, it is obviously applicable to all screen-plates. The screen-plate should be developed as usual, but not reversed, so that a negative in complementary colors is obtained. The positives used as print-plates should be obtained from the complementary negative image in the camera by green, red and blue light, using the normal tri-color filters with panchromatic plates for the red and green and an ordinary for the blue. When working with a camera for enlargement or reduction, the glass of the screen-plate must face the lens for the ordinary pinatype process. But for the modified method the glass should be turned from the lens, as in this case the transparencies themselves are used as print-plates. It is better to use a printing frame, and if a fixed distance and light-source be used, then any number of transparencies can be made, if the ratio of the filters is known. This ratio is not the same as for daylight ; in the former case the exposure for the red filter is the least. The developer should, for preference, be hydroquinon, with a good dose of bromide, so as to work clean and give good density.
The transparencies have a certain grain, which is most pronounced in the case of the blue negative; but this is no disadvantage, and if the plates are fully or slightly overexposed, so as to suffer a little from halation, the image is practically converted into a continuous surface, and the grain is negligible in the finished print. As the screen-plates only give at their best, one-third of the color values of the original, it might be thought that the prints would appear flat and degraded. This, however, is not so, and the result is due to the scattering from the grains of the image, and to the